Fiberoptic cardiac catheters are well known in devices which measure the oxygenation of the blood between the heart and the lungs. Typically, a fiber-optic catheter injects into the blood stream light beams of two distinct wavelengths, one of which lies in the red color band and the other in the infrared color band. These signals are reflected and refracted by blood cells, and separate R and IR signals are obtained at the output of the catheter. Because the amplitude of both the R signal and the IR signal is affected, among other things, by artifacts such as clots or flow patterns, the oxygenation of the blood has traditionally been measured by generating an R/IR signal in which the artifacts cancel out. Oxygenation percentage is a known function of the R/IR ratio, and the oxygenation percentage can thus be measured.
One of the parameters which needs to be monitored is the presence or absence (and, to a lesser degree, the amount) of blood flow which is a medically important indication of the heart action and also an indication of whether or not the catheter field of view being examined is blocked by clots or if the catheter is mispositioned. In the prior art, various methods have been used to determine the flow rate. All of these methods required the use of apparatus other than the fiberoptic catheter itself. Also, the heart action was generally monitored by means of an EKG. The EKG, however, indicates only electric impulses to the heart muscle and does not reflect the actual pumping action of the heart muscle which, in a sick patient, is not necessarily the same.